Hariman Efendi, Nirm 01.4.3.13.0277. The function of farmers in improving the productivity of rubber plants (Hevea brasillensis). The purpose of this research is to study the level of influence of productivity improvement of rubber plant by farmers and the relationship between (learning class, workshop, production unit, improvement of rubber plant productivity). This research was conducted in Pengabuan District of Tanjung Jabung Barat Regency in April until May 2017. Data collection method was interview method using questionnaire to 35 respondent sample, sampling method using probability sampling method with random sampling type sample. The result of the study shows that the function of farmer group in increasing the productivity of rubber plant is still low that is 44.5% percent, it is obtained based on the result of multiple linear regression test where the value of Adjusted R Square is 0,494 or 49,40. Test of regresi where each variable that is The function of the group as a learning class with the value of tcount 1,577, the cooperation vehicle with the value of t count 3034 and the function of the farmer group as a production unit with the value of t01,003 has a tcount greater than ttable (-2.040).